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Counting individual photons (view source)
Revision as of 20:53, 19 April 2007
, 20:53, 19 April 2007no edit summary
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== Poster from Westport Science Fair ==
−{|
−||[[Image:Poster_v1_(main).JPG|thumb|150px|main poster]] ||[[Image:Poster_v1_(center_top).JPG|thumb|150px|center top]] ||[[Image:Poster_v1_(center_bottom).JPG|thumb|150px|center_bottom]]
−|}
−== Measured pulse photon count ==
−[[Image:Pulses_Detected.JPG|thumb|150px|Data]]
−At the right is a snapshot of the pulses produced by a hybrid photodiode (HPD, blue trace) illuminated by a blue light-emitting diode (LED, yellow trace). The average number of photons detected by the HPD per pulse is computed by taking the integral of the charge in a single pulse and dividing it by the average charge per photoelectron in the HPD. The manufacturer (DEP, Netherlands) specifies that the HPD collects 2700 ''e''<sup>-</sup> of charge per photoelectron produced in the cathode. The signal from the HPD was not amplified. It was measured in Volts by the oscilloscope with a 50Ω terminating resistor. The blue trace in the figure displays 20 mV per division, which becomes 0.40 mA / division after dividing by R=50Ω. Visually integrating the red shaded area in the figure gives about 6.5 squares. Each square is 0.40 mA * 250 ns = 100 * 10<sup>-12</sup>C. The charge of each electron is 1.6 * 10<sup>-19</sup> C, so this integral is 600 million collected electrons. Dividing by 2700 collected electrons per photoelectron gives 230,000 detected photons per pulse.
−:<math>\int\ {f(x)}\, dx \approx 230000\ photons</math>
* [[Method for determining how many photons are in a pulse]]
* [[Method for determining how many photons are in a pulse]]
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